154 EULOGY ON GAY-LUSSAC. 



X)eratui'es, evaporated when the apparatus was submitted to high temper- 

 atures; that it increased, therefore, without any means of detecting it, the 

 volume of the elastic fluid upon which they desired to operate. I point 

 out this cause with the more confidence that it is now established that 

 the glasses, according to their composition, and even according to their 

 degree of annealing, are diversely hygrometrical ; so that the degree of 

 heat which would cause complete desiccation in one of these glasses 

 would be insufficient when operating in another apparatus. Gay-Lussac 

 had perfectly understood the effect that hygrometric vapor should pro- 

 duce, and he attributed to this cause the errors of his predecessors. 

 Therefore, it was in following with a little more precaution in the paths 

 traced by our friend that this error of ^ imputed to him was discovered, 

 an error which could do no real injury to the just and legitimate repu- 

 tation for exactness which this learned physicist had acquired and which 

 subsequent works so fully justified. 



When Gay-Lussac was occupied with the numerical determination of 

 the dilatation of elastic fluids by heat, our most skillful physicists thought 

 that different gases have different co-efficients. Witness, for example, 

 what Monge says, which I quote from his memoir on the composition of 

 water : " Elastic fluids are not all equally dilatable by heat." Gay-Lussac 

 found within the limits to which his experiments were confined that this 

 was an error. Since then there has been a return to the first opinion. 

 Indeed, it is almost a consequence of the fact verified by Davy, and espe- 

 cially by our colleague, M. Faraday, that gaseous bodies can be liquefied, 

 and under pressures different for each one of them. 



SOCIETY OF ARCUEIL — MEMOIRS ON MAGNETISM — LAWS OF GASEOUS 

 COMBINATIONS — CATHETOMETER. 



In 1807 Berthollet formed a private scientific society, composed of a 

 small number of individuals and called the Society of Arcueil, after the 

 commune, in the neighborhood of Paris, in which the country-seat of 

 this illustrious chemist was situated. Gay-Lussac, as may be readily 

 imagined, was one of the first members of the new society. Before pro- 

 ceeding further, let us say a few words about the criticisms to which this 

 kind of dismemberment of the first class of the institute formerly gave 

 rise. It was eminently flattering to young dehutants in science to have 

 as chief judges and counselors in their labors men of European celeb- 

 rity, such as Lai)lace, Berthollet, Humboldt, &c. ; but could it be asserted 

 that preconceived ideas to which the cleverest minds mofe readily aban- 

 don themselves in an intimate reunion, so to speak, than before a pro- 

 miscuous public, had not a tendency to arrest the spontaneity of genius 

 and repress its researches below a conventional level? On the other 

 side, might not the desire to give evidence of fertility of mind, in the 

 presence of the most famous scientists, sometimes lead enthusiastic 

 spirits to venture U])on bold theories ? 



Whatever may be thought of these doubts, which I mention with 



